Fracture of modified epoxy resin at high loading rates

Sahraoui, S.; Lataillade, Jean-Luc; Pouyet, J.; Skhiri, N.

doi:10.1016/0142-9418(87)90023-7

Cited by 9 publications

(6 citation statements)

References 9 publications

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“…Similar results have been reported. 25 Concerning the difference in the effect of Desmophen 800 and 1200, this might be due to the structure of both polyols. Desmophen 1200, having a higher molecular weight, thus longer molecular chains with minor ramifications, will have more chance for better interactions with the resin and higher crosslinking density, resulting in better mechanical properties.…”

Section: Fractographymentioning

confidence: 96%

Toughening of epoxy resin using hydroxyl-terminated polyesters

Harani

Fellahi

Bakar

1999

J. Appl. Polym. Sci.

107

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Epoxy resins are increasingly finding applications in the field of structural engineering. A wide variety of epoxy resins are available, and some of them are characterized by relatively low toughness. Several approaches to improve epoxy resin toughness include the addition of fillers, rubber particles, thermoplastics, or their hybrids, as well as interpenetrating networks and flexibilizers, such as polyols. It seems that this last approach did not receive much attention. So in an attempt to fill this gap, the present work deals with the use of hydroxyl-terminated polyester resins as toughening agents for epoxy resin. For this purpose, the modifier, that is, a hydroxylterminated polyester resin (commercially referred to as Desmophen), which is a polyol, has been used at different concentrations. The prepared modified structure has been characterized using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) prior to mechanical testing in terms of impact strength and toughness. Two types of Desmophen (800 and 1200) have been used as modifiers. The obtained results showed that hydroxyl-terminated polyester improves the epoxy toughness. In fact, the impact strength increases with Desmophen content and reaches a maximum value of 7.65 J/m at 10 phr for Desmophen 800 and 9.36 J/m at 7.5 phr for Desmophen 1200, respectively. At a critical concentration (7.5 phr), Desmophen 1200 (with higher molecular weight, longer chains, and lower branching) leads to better results. Concerning K c , the effect of Desmophen 800 is almost negligible; whereas a drastic effect is observed with Desmophen 1200 as K c reaches a maximum of 2.41 MPa m 1/2 , compared to 0.9 MPa m 1/2 of the unmodified epoxy prior to decreasing. This is attributed to the intensive hydrogen bonding between epoxy and Desmophen 1200, as revealed by FTIR spectroscopy. Finally, the SEM analysis results suggested that the possible toughening mechanism for the epoxy resin being considered, which might prevail, is through localized plastic shear yielding induced by the presence of the Desmophen particles.

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Section: Fractographymentioning

confidence: 96%

Toughening of epoxy resin using hydroxyl-terminated polyesters

Harani

Fellahi

Bakar

1999

J. Appl. Polym. Sci.

107

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“…This drastic improvement might be the result of the obtained complex graft IPN. 35 The above arguments, distance between knots, flexibility, crosslinking density, and grafting can be used to explain this improvement in toughness. Another observation is that grafting seems to stabilize the morphology, to reduce phase separation, as indicated by the relative continuous increase in impact strength and K c (Figs.…”

Section: Mechanical Propertiesmentioning

confidence: 98%

Toughening of epoxy resin using synthesized polyurethane prepolymer based on hydroxyl-terminated polyesters

Harani

Fellahi

Bakar

1998

J. Appl. Polym. Sci.

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Epoxy resins are increasingly finding applications in the field of structural engineering. A wide variety of epoxy resins are available, and some of them are characterized by a relatively low toughness. One approach to improve epoxy resin toughness includes the addition of either a rigid phase or a rubbery phase. A more recent approach to toughen brittle polymers is through interpenetrating network (IPN) grafting. It has been found that the mechanical properties of polymer materials with an IPN structure are fairly superior to those of ordinary polymers. Therefore, the present work deals with epoxy resin toughening using a polyurethane (PU) prepolymer as modifier via IPN grafting. For this purpose, a PU prepolymer based on hydroxyl-terminated polyester has been synthesized and used as a modifier at different concentrations. First, the PU-based hydroxyl-terminated polyester has been characterized. Next, an IPN (Epoxy-PU) has been prepared and characterized using Fourier transform infrared (FTIR) spectroscopy, thin-layer chromatography (TLC), and scanning electron microscopy (SEM) prior to mechanical testing in terms of impact strength and toughness. In this study, a Desmophen 1200-based PU prepolymer was used as a modifier at different concentrations within the epoxy resin. The results also showed that, further to the IPN formation, the epoxy and the PU prepolymer reacted chemically (via grafting). Compared to virgin resin, the effect on the mechanical properties was minor. The impact strength varies from 3-9 J/m and K c from 0.9 -1.2 MPa m 1/2 . Furthermore, the incorporation of a chain extender with the PU prepolymer as a modifier into the mixture caused a drastic improvement in toughness. The impact strength increases continuously and reaches a maximum value (seven-fold that of virgin resin) at a modifier critical concentration (40 phr). K c reaches 2.5 MPa m 1/2 compared to 0.9 MPa m 1/2 of the virgin resin. Finally, the SEM analysis results suggested that internal cavitation of the modifier particles followed by localized plastics shear yielding is probably the prevailing toughening mechanism for the epoxy resin considered in the present study.

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“…The load-time and the deflectiontime curves are recorded on the numerical oscilloscope and then analyzed on a personal computer. In dynamic loading, the direct measurement of the specimen deflection by this optical equipment (based on Doppler effect) is more adequate then the measurement the hammer (or projectile) displacement used in the literature [9,10]. The PMMA Charpy specimens (Fig.1) have the dimensions (40x10x10 mm 3 ) and 55 mm for the total length and different crack lengths a (varying between 2 and 5 mm).…”

Section: -Experimental Methodsmentioning

confidence: 99%

“…Future investigations can study the limitation of this approach for high rates of loading. Table : Young modulus versus strain rate and impact velocity [9] Figure 1 …”

Section: -Conclusionmentioning

confidence: 99%